OK, here goes.
I do a fair bit of AE and C4D work as well as standard editing in Adobe CC and some older projects in FCP 7.x.
I currently own a Mac Pro 3,1 with dual quad core 3.0 GHz and 16GB RAM and a Quadro 4000 Mac graphics card. It's pretty long in the tooth.
I've contemplated purchasing a Window PC with i7 4930 CPU, etc. from ADK.
However, I've been reading up on the new Haswell-E that's supposed to come out Q3/Q4 of 2014. There is a lot of hype out there about how this is a 'game' changer for PCs.
Here's the deal. I need something now. I'm contemplating purchasing something like this: Apple Mac Pro 3.46GHz 6 Core QX 5.1 16GB RAM as I'll always have a Mac in my office even if I eventually go the PC route. I'd use this as a stop-gap.
Then, when Haswell-E comes out, get a PC.
I could wait for the new MacPro, but I really need something now as I have 2-3 project over the next month or so where I could really use a speed boost.
My suggestion would be to go with the 4930k system now.
For me, considering your situation, it even sounds like a no-brainer!
1) PCs are better aligned with the proper hardware to do video editing now and likely into the forseeable future.
Note: Apple owned the prosumer video editing space at one time, but those days are over. Steve Jobs was big on doing "end-to-end" solutions where Apple controlled all aspects of the hardware, software, codecs, etc. And with the iPhones and iPads they still do maintain a lot of control and those remain very compelling solutions where they compete. For video, composting, etc. however, PCs are arguably doing a lot better than Apple at all price-points to run Adobe video editing and other high-powered composting software. PCs provide dual-Xeon solutions now, affordable nVidia cuda GPUs, lots of drive expandability, etc. The list goes on and on.
2) There is always a newer faster technology that is months away. Today's PCs really rock for what you are doing.
3) If you go with a PC now, you can upgrade significant parts of it without throwing the whole system out. Apple will never allow this kind of partial upgrade during the life of your system.
Yeah, that's how I'm leaning at this point, just wish ADK wasn't 4-weeks out on their systems :-)